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J. Biol. Chem., Vol. 279, Issue 13, 12163-12170, March 26, 2004

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Physiological Characterization of Haemophilus influenzae Rd Deficient in Its Glutathione-dependent Peroxidase PGdx^*

Frederik Pauwels, Bjorn Vergauwen, and Jozef J. Van Beeumen

From the Laboratory of Protein Biochemistry and Protein Engineering, Ghent University, K. L. Ledeganckstraat 35, 9000 Gent, Belgium

The chimeric peroxidase PGdx of Haemophilus influenzae Rd belongs to a recently identified family of thiol peroxidases capable of reducing hydrogen peroxide as well as alkylhydroperoxides by means of glutathione redox cycling. In the present study, we constructed a H. influenzae Rd strain, deficient in its PGdx encoding gene (open reading frame HI0572). The mutant was shown by disk inhibition and liquid culture growth assays to exhibit increased susceptibility to organic hydroperoxides. The hampered growth was restored by complementing the interrupted gene on the genome with a replicating plasmid bearing an intact copy of the gene, hereby rejecting the possible influences of polar effects. Elevated levels of hydrogen peroxide scavenging activity, due to the catalase HktE, were measured in the absence of a functional pgdx gene rendering the mutant more resilient against hydrogen peroxide. On the other hand, after initiation of the stationary phase, aerobic cultures of the pgdx mutant were practically devoid of living cells, whereas wild-type counterparts retained viability. This observed feature was alleviated by complementation with the functional gene or with the addition of catalase.

Received for publication, November 3, 2003

^* This work was supported by the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT, Grant 3072) (to F. P.) and by the Fund for Scientific Research-Flanders (FWO, Grant 3G003601) (to J. J. V. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Laboratory of Protein Biochemistry and Protein Engineering, Ghent University, K. L. Ledeganckstraat 35, 9000 Gent, Belgium. Tel.: 32-9-264-51-09; Fax: 32-9-264-53-38; E-mail: Jozef.vanbeeumen{at}UGent.be.

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